Avian wing proportions and flight styles: first step towards predicting the flight modes of mesozoic birds.

Xia Wang,Alistair J Mcgowan,Gareth J Dyke

doi:10.1371/journal.pone.0028672

Xia Wang, Alistair J Mcgowan + Show 1 more

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https://doi.org/10.1371/journal.pone.0028672

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Abstract

We investigated the relationship between wing element proportions and flight mode in a dataset of living avian species to provide a framework for making basic estimates of the range of flight styles evolved by Mesozoic birds. Our results show that feather length (f prim) and total arm length (ta) (sum of the humerus, ulna and manus length) ratios differ significantly between four flight style groups defined and widely used for living birds and as a result are predictive for fossils. This was confirmed using multivariate ordination analyses, with four wing elements (humerus, ulna/radius, manus, primary feathers), that discriminate the four broad flight styles within living birds. Among the variables tested, manus length is closely correlated with wing size, yet is the poorest predictor for flight style, suggesting that the shape of the bones in the hand wing is most important in determining flight style. Wing bone thickness (shape) must vary with wing beat strength, with weaker forces requiring less bone. Finally, we show that by incorporating data from Mesozoic birds, multivariate ordination analyses can be used to predict the flight styles of fossils.

Highlights

The timing and sequence of events that led to the origin and subsequent evolution of flapping flight in birds remains an important unanswered question in vertebrate evolutionary biology
The error bars for groups ‘CF’ and ‘flapping and soaring’ (FS)’ do not overlap, differences in these values are not significant enough to pass the Hochberg multiple comparisons tests (HMCT) (P = 0.062); differences detected by ANOVAs must be attributable to differences between the other two groups
As our analyses show that mn length is closely correlated with wing size, we attempted to infer the flight styles of fossil birds based on the plots of fprim/ta, Principal Components Analyses (PCA) and Discriminant Function Analyses (DFA) (Tables 1, 2; figures 3, 4)

Summary

Introduction

The timing and sequence of events that led to the origin and subsequent evolution of flapping flight in birds remains an important unanswered question in vertebrate evolutionary biology. Unlike other vertebrate groups that evolved powered flight (bats and pterosaurs), the leading edge of the avian wing is comprised, to a large part, of feathers which are less likely to fossilize. Little is known about how the proportions of the avian wing evolved [6] despite recent discoveries of numerous non-avian theropod dinosaurs with birdlike feathers [7,8,9]. A ‘functional wing’ (total arm, ta) in non-avian dinosaurs and birds is comprised of the forelimb bones (i.e. humerus (hu), ulna (ul)/radius(ra) and manus (mn)) and the primary feathers (fprim). The evolution of wing proportions in theropod dinosaurs and Mesozoic birds has been studied by simple analyses of specimens with feathered arms [6]

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